Improvement in duplex telegraphs



T. A.. EDISON. :DUPLEX TELEGRAPH. y No..178,zz1.. Patented May 30,1875.

WLARIZED REL" y'lli-#Humanimma? 'IHHNIIINII Nl. t,

W qmffw/a 4 'a y l Wg/w N 4New'Jersey, have invente Unrrnu STATES 'PATENT QFFIGE THOMAS A. EDISON, OF NEWARK,.NEW JERSEY, ASSIGNOR OF' OHNE-HALE1 HIS RIGHT TO GEORGE B. PRESOOTT, OF- NEW YORK'OITY.

IMPRoviaMeN-r IN `'mum-:x TELEeRAP'Hs.

Specification forming part of Letters Patent No. 178,221., dated May 30, 1876; application filed September 1, 1874.

To all whom it muy concern:

Be it known that I, THOMAS A. EDISON, of Newark, in the county-of,` Essex and State of an Improvement in Duplex Telegraphs, of which the following is a specification: j

I" make use of a compound induction-coil, through whichthe currents pass, and those from the sending -station are balanced, but lthe current from the distant station is operativer' .The helix a surrounds the central part Vof the core that passes through the electromagnets band c; hence a secondary or induced current is set up in the helix a only when there is an excess of current in one of the helices b or c, because if the current acting in b is equal to that acting in c, andthe helices are properly wound, the magnetizing actions of the helices on the core will neutralize each other, andthere willnot be any secondary or induced currentin a; but when the current in one helix is. greater than that in the other, the core will be magnetized, and a secondary current set up in the helix a. y

'I avail of this feature of the compound dif-- .ferential induction-coil to operate a duplexltelegraph instrument, by causing the current at the sendingstation, where this compound ldiiferential instrument is placed, to divide and act equally in both b and c,- but when the cur- 'rentfrom the distant station increases the energy of the hel-ix b, then the induction or secondary current set up in the helix a magnetizes.the core suieiently to set upa current ina.

The current in a operates in the polarized `magnetf to open and close the local circuit g,

in .which is placed the receiving or sounder instrument h.

When the p'ulsation passing along the line k from the distant station ceases, the core of the helix b delnagnetizes, and in so doing sets up a second induced current in a of opposite polarity to the first, andv that acting in the polarized magnet f instantly throws the contactpoint of the armature the other way and opens .the local circuit.

These operations in the compound dii'erential induction-coil being borne in mind, it now becomes necessary to explain the manner of sending through such coils without producing any action on the helix a. v

The key l in the local circuit to the magnet m operates the lever n, that contains an insulated springcloser, 3, acting against the circuit-point 4, and the hook end 5 of the lever n, so that when l u moves the spring 3 into contact with 4, closing the circuit from-the battery o., through 4 3 and thewire 6, to the helices b and c, and at the same time breaking the contact of 3 and 5, and hence 'cutting out the ground-wire 8 from the lever a; but the moment the lever n returns to its normal position by the demagnetizing of m, the spring 3 closes the circuit at5, just before separating from 4; hence there is Valways a metallic circuit complete for the pulsation coming from the distant station, whether the circuit ot' the sending-battery o is opened or closed.

In order to'- balance the action lof the sending-curreilt, that divides at 10, and passes through b and y c, l introduce, in connection with the helix c, an artificial line equal in resistance and conditions tothe line k, hence compellingan equal current to pass 4through b and c.- To eiect this the resistancer is placed in the ground-connection from c, which resistance should be adjustable,| so that the rheostat or resistance r equals the line; and

in order to set up in c a counter magnetism equal to that set up in b by the static from the line, placed in a shunt that passes around c.

By this construction of compound differen- 'tial inductioncoil', and the arrangement of the connections, the inductive effects ot' pulsations from the'sending-instrument are balanced and neutralized, while the pulsations. from the distant station operate'- the receiving-instrument.

I claim as myinvention- 1. The compound l differential inductioncoils a b o, in combination with the polarized relay f and the circuit-connections, substantially as set forth. i

2. The artificial line, composed of the rheostat4* and magnett and ground-connection, in combination with the compound inductioncoil and line-connections, substantially as set forth.

Signed by vme this 19th day of August, 1874.

THOS. A. EDISON.

Witnesses:

Unas. H. SMITH, y Guo. T. PINCKNEY.

the key l is closed, the lever I make use of the electro-magnet t,V 

